The invention relates to a throttle body with a Torquer drive, in which the rotor of an electric drive motor is seated directly on the shaft of the throttle butterfly. The invention furthermore relates to a method for assembling such a throttle body.
In comparison with motors coupled to the throttle-butterfly shaft via transmission stages, such an arrangement of the rotor requires very few components and also requires less installation space. However, allowance must be made for the fact that the throttle butterfly is excited to vibrate. Whereas, in the case of solutions with a separately mounted rotor, a pin which is anchored in the housing of the throttle body and engages with a defined play in a circumferential groove on the throttle-butterfly shaft, may be sufficient for the axial retention of the shaft, the high mass of the rotor in a throttle body with a Torquer drive leads to very high unit surface loading under the vibrational movements, with the result that wear of the axial contact surfaces and hence an increase in the axial play can rapidly occur given small supporting surfaces. The throttle butterfly becomes stiffer and, in the most extreme case, may stick. As a further problem with the axial fixing of the throttle-butterfly shaft, there is the fact that there is only a limited amount of axial installation space available since, in addition to the axial retention means and the rotor, it is also necessary to provide a potentiometer for detecting the actual position of the throttle butterfly and the rolling-contact bearings for supporting the throttle-butterfly shaft in the throttle housing. Although it is possible, in principle, to arrange these elements on both sides of the throttle butterfly in the housing, this makes assembly more difficult.
The object of the present invention is to provide an axial retention means for a throttle body with a Torquer drive which can withstand the higher stresses and is simple to assemble.
According to the invention, the object is achieved by a throttle body with a Torquer drive, in which the rotor of an electric drive motor is press-fitted directly on to the shaft of the throttle butterfly, an axial retention means in the form of a retaining washer being provided between the throttle butterfly and the rotor, said retaining washer being fixed axially on the shaft or on a throttle housing and engaging with a defined axial play in a gap on the other element, and the two housing-side axial contact surfaces of the retaining washer being formed by a fastening plate screwed to the housing and by a stop provided on the housing.
The solution according to the invention offers first of all the advantage that the retaining washer provides large-area contact with the two flanks of the gap, with the result that the unit surface loading and hence wear is low despite the increased inertia forces due to the electric-motor rotor seated on the throttle-butterfly shaft, thereby ensuring a constant axial play over the service life.
Axial fixing on the housing by means of a screwed fastening plate furthermore ensures that the axial installation space required is only very small, making possible the arrangement of the axial retention means between the throttle butterfly and the rotor, which is advantageous for assembly reasons, with a short and hence rigid throttle-butterfly shaft.
In a first preferred embodiment of the invention, the retaining washer is seated with a defined axial play on the shaft in a circumferential groove and is fixed without axial play on the housing side by means of the fastening plate.
In this embodiment, the axial play can be maintained very accurately with low outlay in terms of manufacture since, for a known thickness of the retaining washer, all that is required is to cut a circumferential groove of defined width into the circumference of the throttle-butterfly shaft. The retaining washer can, for example, be designed as a C washer and be inserted laterally into the groove or be implemented by means of two half-shells.
The fastening plate and the retaining washer can furthermore be of one-piece design, the shaft opening being designed in the shape of a keyhole. The advantage of this embodiment lies in the further slight reduction in the axial installation space and in the reduction in the number of parts. Here, the widened region of the keyhole serves for the introduction of the shaft before installation in the throttle housing. A discontinuous design of the keyhole opening is also conceivable.
As an alternative to a circumferential groove provided in the shaft provision is made in another embodiment of the invention for the retaining washer to be fixed axially on the shaft circumference and the gap at the housing to be defined by an axial stop and one flank of the fastening plate. The axial stop can be provided with a contact disk.
In this variant, the axial play is obtained from the difference between the axial spacing of the housing stop from the contact surface of the fastening plate and the thickness of the retaining washer. The firm seating of the retaining washer on the throttle-butterfly shaft is preferably established by means of a welded joint, a press fit also being possible in principle, although this may require a thicker retaining washer to ensure that the washer is seated securely on the shaft.
The present invention also relates to a method for assembling a throttle body of the type described above. According to the invention, the throttle body is first fully preassembled, and the rotor is press-fitted on to the shaft only at the final stage before the throttle housing is closed.
The advantage of this assembly method is that the throttle-butterfly shaft can be inserted from the rotor side into the bearings, which are generally designed as needle bearings, and the axial retention means and the potentiometer can then be installed without being hindered by the rotor. The high weight of the rotor would furthermore make handling during assembly more difficult.